Although many people say this book inspired the film "The Truman Show", Expect far more than that in this book. Ragle Gum is not merely another Truman Burbank. He is contained in a world of illusion not for the purposes of keeping others entertained, he has something dreadfully important to do, something somehow wrapped up with the daily puzzle he solves in the newspaper.
This book is about turning around the perception of the protagonist (Ragle Gum) and that of the reader again and again. Is Ragle going psychotic and paranoid with his suspicion that reality doesn't quite seem to make sense that everything seems to be constructed for his benefit? Or is he instead actually recovering his sanity? And then when he penetrates through to another layer of reality, is what he was doing critically important to save lives or is he merely furthering the cause of tyranny?
I'm treading dangerously close to spoiling the plot but I feel that I've held back from crossing that line by being suitably vague and also because I think a reader of average intelligence will see most of the plot turns coming well ahead of time.
Doesn't quite mess with your head as much as some of his later novels so is perhaps a good place to start as a PKD newbie. Still well worth a read for more experienced PKD fans.